The present invention relates to the control of a gas turbine power plant and, more particularly, to reliable and bumpless transfers between the primary control system of such a plant and a backup control system. Transfer is effected and enhanced by tracking a plurality of functionally identical, but independent signals.
Local maintenance or backup control systems for both gas and steam turbine plants are known in the prior art. Typically, such backup systems achieved their stated purpose through excessive redundancy or a relatively high degree of operator intervention. Alternatively, minimum backup capability was provided, i.e., only one or two critical plant parameters were controlled in the backup mode, but at a cost of control versatility and plant availability. Furthermore, certain functions such as alarm reset capability were either operator dependent or unavailable.
Due to the increasing use of computer implemented primary control systems for power plants, the need for backup control has become pronounced. Remote placement of power plants, for example, required backup capability. The need for maintenance of the primary control system, without loss of plant availability, also contributed to the need. Moreover, customer demands for overall plant reliability and generating availability dictated enhanced backup capability.
Thus, there existed a pronounced requirement for a backup control system which would do many of the things suggested in or taught by the prior art systems, but one which would be improved thereover and be able to function independently of the primary control system in remote locations for long periods of time with enhanced functional capabilities in an efficient, relatively inexpensive and reliable manner. More specifically, the need also existed for a backup control system which could be armed preparatory to assuming control, but which would draw only minimal power in such a state thereby increasing the life of many of its components and reducing operating costs. Further, the usefulness of such a backup control system would be increased by giving it the ability to perform additional functions, such as automatic alarm circuitry reset, thereby reducing operator involvement and operating cost.
In addition, the need existed for a backup control system which would accept a transfer only when it could be effected in a bumpless manner. Further, the need existed for capability in such a backup control system for preventing transfer of control command back to the primary system if it could not be achieved in a bumpless manner.